Lzx depacked refactor and cleanup

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Merge branch 'master' of ssh://git.code.sf.net/p/xmp/libxmp
[test] Add tests for Unic/Unic2 formats

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Add test for Mod's Grave loader

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
[test] Add test for 15-instrument mod files

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>